The present invention relates to the measurement of contour features of surfaces and, more particularly, to a system using optical triangulation to measure a selected contour feature of a surface, including surfaces where contact of the apparatus or gage with the surface may contaminate or distort the surface, and to determine the conformance of the contour feature to a predefined specification.
Component parts for high performance machinery, such as those used in gas turbine engines for aircraft propulsion and the like, are manufactured to precise specifications and to avoid sharp edges and tight corners because such features are areas where stress concentrations can occur and increase the possibility of formation of a crack or other defect. Component part edges are, therefore, typically chamfered, curved to form a radius or otherwise contoured to dull the sharp edge to reduce the probability of crack formation and to improve fit between different components. Accurate measurement of contour features, such as edge and corner contours, is, therefore, important to ensure the quality of the component and its ability to resist crack formation and to fit properly with mating parts.
Presently used methods and devices for measuring the contour of edges and corners include hand-held contour gages, which are pre-cut to the radius or contour expected to be measured, impressions of the radius or contour expected to be measured, optical comparators, mechanical tracers and coordinate measuring machines. Contour inspection with pre-cut radius or contour gages involves placing gages of known radii or contour in contact with the component part surface and back illuminating both the part and the gage. If the contour of the part and the gage coincide, no light will pass between the part and the gage. If variations exist between the contour of the gage and the part, light will be allowed to pass between the gage and the part in varying degrees depending upon the extent of the variation. The extent of the error in the contour of the part is then determined by an inspector and is subject to his judgment. Thus, such measurements or inspections are dependent upon the skill and vitality of the inspector and operator and may be subject to error and difficult to replicate. Additionally, the use of pre-cut radius or contour gages becomes impractical with significant loss of accuracy as the contours being measured become smaller and/or include compound radii or contour features.
Simple and compound contour features can be measured by forming an impression of the contour surface feature using dental wax or other suitable material. The wax impression is then evaluated using an optical comparator or a mechanical tracing device which is usually located in an area removed from the component under inspection. The comparator or mechanical tracer utilizes a template or screen with the desired contour at the proper magnification for comparison with the wax impression. Again, this method and apparatus is dependent upon the skill and judgment of the operator or inspector and may be subject to inaccuracies. If the component part to be measured is movable, the contour feature may be measured directly on the optical comparator or tracer. The component part must be fixtured on the comparator or tracer which can represent quite a challenge if the component is large or has an unusual shape. This method, while avoiding any inaccuracies associated with forming the wax impression of the system previously described because the part is measured directly, would, however, still suffer from the same disadvantages described hereinabove.
Coordinate measuring machines are another well known device for measuring surface contour features and provide relatively accurate results when measuring large radii. These devices, however, are expensive, have slow processing rates and are not easily adaptable to a production environment.
Critical components with complex geometries, such as those used in gas turbine engines for aircraft propulsion, add complexity and present a challenge with respect to the measurement of edge and corner contours by using any of the devices or methods described hereinabove. The surfaces of such components may contain compound curvatures, edges and corners which are difficult to access, and the components themselves may be difficult to manipulate and move from one location to another for ease of securing measurements.
Therefore, a need exists for a portable, highly maneuverable hand-held contour measuring device which can provide fast and accurate results and is not subject to the foregoing disadvantages.
It is, accordingly, a primary object of the present invention to provide a novel apparatus for measuring the contour of a surface which is not subject to the foregoing disadvantages.
It is another object of the present invention to provide a hand-held highly maneuverable device which permits quick and accurate measurement of a contour feature of a surface.
It is a further object of the present invention to provide an apparatus which permits selective measurement of a plurality of different contour type features.
These and other objects of the invention, together with features and advantages thereof, will become apparent from the following detailed specification when read with the accompanying drawings in which like reference numerals refer to like elements.